ABSTRACT
Iron phosphate-based coating and iron silicate-based coating were used to inhibit the oxidation of sulfide minerals in rainy and submerged environments. The inhibiting effectiveness of coating agents on the oxidation of iron sulfide minerals was investigated using pyrite and rock samples resulting from acid drainage. The film formed with both surface-coating agents was identified by pyrite surface analysis. It was also confirmed that the formation of coatings varies depending on the crystallographic orientation. The inhibitory effects under rainy and submerged conditions were investigated using column experiments. Submerged conditions accelerated deterioration compared to that under rainy conditions. Iron phosphate coating had a significantly better oxidation-inhibitory effect (84.86-98.70%) than iron silicate coating (56.80-92.36%), and at a concentration of 300 mM, H+ elution was inhibited by more than 90% throughout the experiment. Furthermore, methods for effective film formation were investigated in terms of producing Fe3+; (1) application of coating agents mixed with oxidant (H2O2), (2) application of coating agent after the use of the oxidant. In a rainy environment, applying iron phosphate-based coating using the sequential method showed oxidation inhibition effects for cycles 1-9, whereas applying the mixed material showed effects for cycles 9-13. The use of a surface-coating agent after applying an oxidant did not inhibit oxidation. The surface coating agent and the oxidizing agent should be applied as a mixture to form a film.
Subject(s)
Iron , Oxidation-Reduction , Phosphates , Silicates , Silicates/chemistry , Iron/chemistry , Phosphates/chemistry , Acid Rain , Sulfides/chemistry , Hydrogen Peroxide/chemistry , Ferric Compounds/chemistryABSTRACT
Pyrite and other iron sulfides are readily oxidized by dissolved oxygen in aqueous phase, producing acidity and Fe(2+), which causes significant environmental problems. Applications of surface coating agents (Na2SiO3 and KH2PO4) were conducted at Boeun (Chungbuk, South Korea) outcrop site, and their efficiencies to inhibit the oxidation of sulfide minerals were monitored for a long-term period (449 days). The rock sample showed positive Net Acid Production Potential (NAPP = 20.23) and low Net Acid Generation pH (NAGpH = 2.42) values, suggesting that the rock sample was categorized in the potential acid-forming group. For the monitored time period (449 days), field study results showed that the application of Na2SiO3 effectively inhibited the pyrite oxidation as compared to KH2PO4. Na2SiO3 as a surface coating agent maintained pH 5-6 and reduced oxidation of pyrite surface up to 99.95 and 97.70 % indicated by Fe(2+) and SO4 (2-) release, respectively. The scanning electron microscope and energy-dispersive X-ray spectrometer analysis indicated that the morphology of rock surface was completely changed attributable to formation of iron silicate coating. The experimental results suggested that the treatment with Na2SiO3 was highly effective and it might be applicable on field for inhibition of iron sulfide oxidation.
Subject(s)
Environmental Restoration and Remediation/methods , Iron/chemistry , Oxidation-Reduction , Sulfides/chemistry , Microscopy, Electron, Scanning , Phosphates/chemistry , Potassium Compounds/chemistry , Republic of Korea , Silicates/chemistry , Spectrometry, X-Ray EmissionABSTRACT
RATIONALE: Stable isotope compositions of natural waters, such as seawater, glaciers and basinal brines, can provide valuable information about Earth's hydrological cycle and its evolutionary history. However, a high concentration of dissolved ions in some natural waters hinders an accurate analysis of their oxygen isotope composition. A laboratory study was carried out in order to provide guidelines on how to resolve this analytical difficulty. METHODS: CO(2) gas was equilibrated with saline aqueous solutions of various chemical compositions at 25 °C. Subsequently, the oxygen isotope composition of the CO(2) was determined at different equilibration times using a dual-inlet isotope ratio mass spectrometer in order to evaluate the oxygen isotope salt effect and the rate of oxygen isotope exchange between CO(2) and the saline solution. RESULTS: Using the experimentally determined oxygen isotope salt effects of aqueous chloride and sulfate solutions, an empirical method for the prediction of the oxygen isotope salt effect of a 1.0 molal chloride or sulfate solution was proposed. The rates of oxygen isotope exchange between CO(2) and saline solutions were also examined. Our experimental data indicates that the sequence of the oxygen isotope exchange time is as: MgSO(4) > CaCl(2) ≈ Na(2)SO(4) > NaCl > MgCl(2) > KCl > H(2)O. CONCLUSIONS: The isotope salt effect and the kinetics of isotope exchange must be taken into account when the oxygen isotope composition of a saline aqueous solution is determined using the CO(2)-H(2)O equilibration method. Our experimental data and the proposed prediction method provide essential guidelines for the accurate δ(18)O analysis of saline aqueous solutions.
